Effect of Cu substitution on structures and electrochemical properties of Li[NiCo1−xCuxMn]1/3O2 as cathode materials for lithium ion batteries

Abstract

This study on Cu-doped Li[NiCoMn] _1/3O ₂ provides support for reusing Cu as a beneficial dopant in the production of metal-doped Li[NiCoMn] _1/3O ₂ from spent LIBs.

Abstract

Copper ions are one of the major associated metal ions present in the precursors of the synthesis of Li[NiCoMn] _1/3O ₂ from the recovery of spent Li-ion batteries by wet chemical processes. To evaluate the feasibility of reusing Cu ²⁺ as a favourable dopant in Li[NiCoMn] _1/3O ₂ instead of as usual removing it as an undesirable impurity, the effect of Cu-doping on the electrochemical behaviour of Li[NiCoMn] _1/3O ₂ is investigated in this work. Li[NiCo _1−xCu _xMn] _1/3O ₂ ( x = 0, 0.02, 0.04, 0.06 and 0.08) is synthesized through two steps, roasting the precursors obtained from carbonate co-precipitation, and their structures and electrochemical performances are systemically investigated. The results indicate that substitution of Co with Cu was successfully achieved without any detectable second phases. The initial discharge capacity of Li[NiCo _1−xCu _xMn] _1/3O ₂ gradually dropped with an increase of x but the rate property and capacity retention were remarkably enhanced. In particular, the capacity retention of the Li[NiCo _0.94Cu _0.06Mn] _1/3O ₂ sample reached 95.87% within 50 cycles at a current density of 160 mA g ⁻¹. CV and EIS revealed that such improvements are ascribed to a higher Li ⁺ diffusion coefficient and lower charge-transfer resistance derived from Cu ²⁺ doping. The results suggest that Cu can be used as a beneficial dopant to partially substitute Co in synthesizing Li[NiCoMn] _1/3O ₂ from spent LIBs instead of having to remove it as an impurity.